Data Communications & Networks

Introduction to

Network Applications &

Network Services

UCCN 1003 (May 2010)

(Lecture 01a)

Common Network Applications

Introducing some common

network applications & screenshots

Internet & Daily Life

• When you access the Internet, do you use the following applications?– Internet Explorer, Firefox,

– Google Mail, Hotmail, Yahoo Mail,

– Yahoo Messenger, MSN Messenger, Skype

– Facebook,

– Online games

– and others….

• Since these applications require the access to the Internet, we refer these applications as network applications.

Microsoft’s Internet Explorer

• Perhaps, the most frequently used network application in your daily life is Internet Explorer.

• You use Internet Explorer to– Check your Hotmail or Google Mail.

– Reading news (e.g. cnn.com)

– Access to Facebook

– Downloading movies, games, etc…

• In fact, Internet Explorer is categorically called a Web Browser.

Web Browser

• By definition: – A web browser is a network application for retrieving, presenting, and

traversing information resources on the World Wide Web.

• The following network applications (web browsers) do the same thing as Internet Explorer:– Google Chrome

– Mozilla Firefox

– Netscape

– Opera

– Safari

– Camino

– Konqueror

– and others….

Netscape 2.0

is The browser that

make the Internet or

World Wide Web

into a world wide

phenomena back in

1996.

Other Web Browsers’ Screenshots

Safari Google Chrome

Other Web Browsers’ Screenshots

Firefox Opera

Instant Messaging

• Perhaps, the second most popular network application beside the web browsers is Instant Messaging.

• Instant messaging (IM) is a form of real-time direct text-based communication between two or more people using personal computers (PCs) or other devices. – More advanced instant messaging software also allow live

voice or video calling.

• Some of the popular instant messaging software:– ICQ

– Skype

– Windows Live Messenger

– Yahoo! Messenger

– Google Talk

– Facebook

– ebuddy

Screenshots of Other Instant Massagers

Other Network Applications

• Besides Web Browser and Instant Messaging, there are other network applications that do:

– Email (Microsoft Outlook, Mozilla Thunderbird)

– File transfer (Ws_FTP, Free Download Manager)

– Remote login (PuTTY, Terra Term)

– Accessing remote database (SQuirreL SQL

Client )

– Internet Relay Chat (mIRC)

– and other …

Email

Microsoft’s Outlook

Mozilla Thunderbird

File Transfer

WS_FTP

Download Manager

Remote Login

• PuTTY, Tera Term, etc

Accessing Remote Database

SQuirreL SQL Client

Internet Relay Chat (IRC)

mIRC (precursor of Instant Messenger)

Question

• What do all these network applications have in common?

– What common features do all these network

application share?

Answer

• In general, these network applications share a common feature among themselves, which is accessing some form of remote information or resources. For example:– Firefox is accessing a web site for web pages.– Outlook is retrieving emails for a “inbox”

– Skype has to gain access to your “list of friends” via login.– Download Managers are used to download movies from

some “file sites.”

– Play online games “World of Warcraft” via a “networked game world”.

• These network applications can be technically called as network client software.

Network Client Software

• The main function of network client software is to access the resource/information in the network/internet known as network services.– All these so-called “network services” are located “somewhere” in the

network or Internet.• Do you know or care where is www.cnn.com or www.msnbc.com?

– Network client software CAN’T exist WITHOUT network services.• Network clients have to talk to network services.

– Client-server HAVE to work in pair.• Known as client-server communication, which is 99% of today’s Internet

traffic.

– Client software can’t communicate with other client software.• You can’t use Web browser to talk directly to another browser.

• Instant messaging has to communicate via a server.

• Like all software applications, all network client software come in two forms:– Command-line & GUI (graphic-user interface)

Review: Network Client Software in Your PC

• Web Browsing: – Firefox, Internet Explorer, Opera

• E-mail: – Outlook, Thunderbird

• Instant messaging: – MSN Messenger, Skype, ICQ, MIRC

• Video and audio streaming: – Real player, Window Media Player, iTune

• Internet telephone: – Skype

• Real-time video conference– Skype, live messager,

Network Services

Introducing some common types of

network services, and the concept

of clients-servers.

Network Services and Server

• Network services provide remote software resources support to the network clients

• Network services are normally reside in network servers.– Network services = software– Network servers = hardware (PC)

• Clients of different operating systems (MAC or Windows) access the same services of the same server– PC or MAC can read the same web page.– Network services are “platform

independent”. (Linux or Windows or Sun)

• Network is the “middle-man” that give communication links between servers and clients.

Data and Information Servers in your life

• When you read cnn.com, – you’re communicating with a web server.

• When you read your yahoo.com mail, – you’re communicating with a mail server (together with a web server).

• When you downloading files from Internet, – you’re communicating with a file server.

• When you’re using msn, or skype, there is a server behind “coordinating” your communication.– When you login to a msn messenger, you’re communicating with a

Instant Messenger server. Through the server, you message is then relayed your friend who is online.

• When you’re playing massively multiplayer online role-playing game, MMORPG (e.g Perfect World)– you’re communicating with a game server.

• When you’re watching on-line video (youtube)– you’re communicating with a video streaming server.

Server and Client - 1

• Server– A computer on the network that

manages shared network resources.

– Usually a more powerful computer with more RAM, Disk Space and Processing Power

• usually but not necessary

• Client– A computer on the network requests

services from another computer on a network.

• Servers provide services• Clients request services• Servers runs on a different set of

software than the clients.• 1 server (or PC) can provide many

services.

Client & Server - 2

• All client software communicate with server– When you are using a web browser, your PC acts as a network client.

– Main task of client software is to “request” service from server

– Clients (web browser) get services (web pages) from servers (web sites).

• Client software don’t communicate with other client software directly.• Client software communicate with other client software via servers

– Mail server, Instant Messenger server

• This type of servers acts as a “middle-man” between the clients.– User of PC1 sends a mail to user of PC0 (stored in mail server)

– User of PC0 reads the mail at the mail server

Differences between Server & Client

• Servers normally runs 24 hours / 7 days.• Clients are “normally” switched off once the users are gone.

• Servers runs “independently” once configured.• Clients runs “dependently” with human users.

• Servers can have 1 monitor, 1 keyboard and 1 mouse connected to multiple CPUs (coordinated via KVM switch)

• Clients have 1 (sometimes 2) monitor, 1 keyboard, and 1 mouse with 1 CPU.

• Server software always “listens”• Client software sends “request” to server on demand.

• Lastly, servers and clients run on different set of software• Server’s software normally runs in the “background”

Two Categories of Servers

• Data and Information Server– Providing data and information

– Pure data server (web server, file server) • When you just read and download only.

– “Middle-man” servers (email server, newsgroup server, instant messenger)• When writing and uploading are involved

• Networking Server– Helping out in the network

– The client side will normally be the operating system (e.g. Windows XP, Linux)

– DNS server, DHCP server, print server

Some Common Servers

• Web Server (data and middle-man)– Providing web pages

• Mail Server (data and middle-man)– Storing and send emails

• File Server (data and middle-man)– Downloading and uploading files

• Print Server (networking)– Managing print queue jobs

• Database Server (data and middle-man)– Providing necessary data to clients

• DNS Server [domain name server] (networking)– Managing corresponding network address with domain name

• DHCP Server [dynamic hosts control protocol] (networking)– Supply IP addresses to PCs with dynamic IP option

• Proxy Server (data and networking)– Acts as an intermediary between external and internal networks,

screening all incoming and outgoing data traffic

• Newsgroup Server (data and middle-man)– Managing newsgroup

Server Software Example: Apache

• You can download it from http://httpd.apache.org/• Store your web page in assigned directory and start the

service– Once you start the service, Apache runs at the “background”.

Some final notes on server & client

• A server can be client at the same time.– You install Apache Web package in your PC, configure it and store

your web page.– You can still use your PC to surf the web (as long as you have the

web browser)– Outsider access your web page at the “background” of PC

(meaning without your knowledge unless you check for it).

• A server can run different services at the same time. A client PC can communicate with different servers (or services) at the same time.– You open Firefox, Outlook, Skype, while playing MMORPG

• However, A client program can normally talk to a type network service at any given time.– You open Firefox to access web page but not remote login.– You open Firefox to access a file server but not a web server at the

same time.

Quiz

Some questions to help your memory

and understanding

True/False Questions

1. Server must run on better PC than client.2. Client always listens to request.3. A pure client PC can provide network services.4. A windows XP PC can be configured as both client and server.5. Client program has to be run at the “foreground” interfacing with

human.6. A web server can’t be a print server at the PC.7. A client program can talk to multiple network services simutenously.8. Client program can’t communicate with another similar client

program directly.9. Server program normally runs at the background without much

interaction with user.10. A dns server and a dhcp server have to be on different machine/PC.

Answer

1. False

2. False

3. False

4. True

5. True

6. False

7. False

8. True

9. True

10. False